Recently, cellular telephones or handsets equipped with a digital camera (also known as “camera phones”) have become available and are a popular item among consumers. By adding a camera functionality to the ubiquitous cellular telephone, consumers are more apt to take digital pictures to share with friends, etc. Furthermore, new camera-enabled mobile applications such as multimedia messaging, visual caller identification, and mobile photo albums have become popular with consumers. These popular applications coupled with the growing worldwide demand for camera-enabled handsets have made mobile imaging an essential feature for handsets in many markets.
Consequently, mobile handsets manufacturers are faced with the need to incorporate the functions of a digital camera into the cellular telephone. Agilent Technologies, Inc., the assignee of the current application, is a market leader in CMOS imaging solutions and a leading supplier of semiconductor solutions for today's highly integrated, feature-rich mobile handsets and offers embedded camera modules for mobile handsets manufactures.
An important component in the camera module is the image sensor integrated circuit that includes a pixel array with a plurality of pixels that are arranged in rows and columns. Each pixel receives light and converts the received light into a corresponding analog signal that represents the received light. Specifically, each pixel in a row is reset to a predetermined signal (e.g., a predetermined reset voltage). The pixels in the row are then integrated for a predetermined time period. During integration, the pixels receive light, which decreases the reset voltage to a signal that represents the amount of light received at the pixel. For example, pixels that have a value close to the reset voltage appear dark in the picture, whereas pixels that have a value close to zero, appear as bright spots in the picture.
One challenge faced by designers is the reduction in the power supply voltage that is caused by consumer demand for longer battery life and longer operating time of the electronic device between charges. Unfortunately, as the power supply voltage is decreased, the dynamic range of the system also decreases.
One approach to increase dynamic range while reducing the power supply voltage is to employ a boost generator that generates a reset voltage (also referred to as a “boost signal”) that is higher than the power supply voltage and provides this boost signal to the pixel array.
However, the design of the boost generator pose significant challenges and introduces issues and design concerns. One problem encountered is that the boost capacitance is fixed and unchangeable after the integrated circuit containing the boost capacitor is manufactured. There are instances where it would be convenient to change the boost capacitance after the fabrication of the integrated circuit. Second, certain image capture situations may benefit from a boost signal with a different level than the fixed boost signal level. Unfortunately, the existing boost signal generators only offer a single boost signal level that is set once the integrated circuit is manufactured.
Based on the foregoing, there remains a need for a programmable boost signal generation method and apparatus that overcomes the disadvantages set forth previously.